Blue Diaper Syndrome and PCSK1 Mutations.

Blue diaper syndrome (BDS) (Online Mendelian Inheritance in Man number 211000) is an extremely rare disorder that was first described in 1964. The characteristic finding is a bluish discoloration of urine spots in the diapers of affected infants. Additional clinical features of the first described patients included diarrhea, inadequate weight gain, hypercalcemia, and nephrocalcinosis. An intestinal defect of tryptophan absorption was postulated as the underlying pathology. However, functional evidence for this theory is lacking. No genetic cause has been identified so far. Here, we report on a boy who presented with neonatal-onset diarrhea, metabolic acidosis, transient hepatopathy, recurrent hypoglycemia, and blue-stained urine spots in his diapers. An ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry analysis of urine samples at different time points demonstrated the constant presence of indigo derivatives, thereby confirming the diagnosis of BDS. Of note, the visibility of indigo derivatives in the urine was highly dependent on the urine's pH. To identify the underlying genetic cause of the disease, whole-exome sequencing was performed, leading to the identification of a homozygous frameshift mutation in proprotein convertase subtilisin/kexin type 1 (PCSK1; NM_000439.4: c.679del, p.[Val227Leufs*12]). PCSK1 encodes prohormone convertase 1/3, and mutations within this gene have been reported as a rare cause of early-onset malabsorptive diarrhea and multiple endocrine dysfunction. In our report, we suggest that BDS can be caused by PCSK1 mutations.